It is well known in the construction and building industry that concrete structures require reinforcement means during the formation of the structures. Such reinforcement means typically are steel reinforcing bars or rods commonly known as "rebar".
The general procedure followed for forming a concrete foundation support structure such as a concrete pier involves drilling or excavating a shaft or hole in the ground at a predetermined location. A reinforcement cage is formed from reinforcing steel and is inserted into the excavated shaft. The reinforcement cage typically is fabricated above ground from a series of elongated steel rebar or similar reinforcement materials. The steel rods are arranged in a substantially parallel cylindrical array and are bound together in this configuration by laterally oriented rebar ties. The rebar ties typically are circular sections of rebar fitted about the parallel steel rods at several locations along the lengths of the parallel rods and tied thereto with conventional tie-wire. Another configuration of the laterally extending rebar ties is a single elongated section of rebar that is wound about the parallel steel rods in a helical configuration. The ties are connected to the reinforcement cage at points of contact between the parallel rods and the rebar ties by tie-wire. The rebar ties hold the parallel rods in an elongated cylindrical cage configuration. The assembled steel reinforcement cage is inserted into the drilled or excavated shaft prior to the pouring of concrete therein.
As the concrete is poured, it is necessary that the steel reinforcement cage be properly centralized and positioned within the excavated shaft in order to form a solid and stable foundation support such as a pier or caisson. A problem faced by drilled shaft contractors is trying to insert the reinforcement cage into the excavated shaft and maintain the reinforcement cage in a centered alignment within the excavation shaft without the reinforcement cage being shifted toward or engaging the side wall of the excavation shaft as concrete is poured therein to form the foundation structure.
In order to solve this problem of maintaining the reinforcement cage in a centered position within the excavated shaft, it is common among drilled shaft foundation contractors to use spacers mounted to the horizontally oriented rebar ties of the reinforcement cages. The spacers engage the side wall of the excavation shaft and prevent the reinforcement cages from shifting toward or becoming engaged with the side walls of the excavated shaft. The spacers maintain the reinforcement structures in a centered position within the shaft, spaced from the side wall thereof.
There are several types of prior art structures used as spacing devices or in common use as spacing devices for the construction of concrete foundation structures. The prior art spacers usually are installed on the reinforcement cage at the building site. The first type of spacer generally used is a simple solid concrete wheel that is formed in the field from waste concrete. These solid concrete spacers typically are circularly shaped with an opening in the middle thereof. A problem with such concrete wheels is that they are heavy and not easy to manipulate and are difficult and time consuming to produce and to install on the rebar ties of the reinforcement cages, as the wheels must be threaded onto the rebar ties and secured in place during the construction of the reinforcement cages. This usually requires the rebar ties to be separated from the parallel rods so that an end of a rebar tie can be telescopically threaded through the central opening of the concrete wheel, and after the wheel has been threaded onto the rebar tie, the rebar tie must be reconnected to the parallel bars. Such an operation usually is very labor intensive and expensive, as it is generally skilled steel workers that are used to construct and install the reinforcement cages.
Other prior art designs have included large plastic open-spoke wheel spacers having slotted openings formed therein. These open spoke wheel spacers are adapted to simply slide over and rest upon the rebar ties of the reinforcement cages. Such open-spoke wheel spacers generally are not very sturdy and are easily twisted and can be easily dislodged from the ties of the reinforcement cage, especially as the reinforcement cages are being inserted into the excavated shafts.
Another type of spacer assembly being used with concrete reinforcement cages is a "sled" design spacer illustrated in U.S. Pat. Nos. 4,627,211 and 4,741,143. Both of these patents illustrate a plastic or concrete sled of a substantially D-shaped design and which is attached to the ties of the reinforcement cage by conventional tie-wire. A problem with such spacers is that, while such spacers might aid in the centering of the reinforcement cage as it is inserted into the excavated shaft, as the concrete is poured into the shaft, the force of the concrete entering the shaft tends to exert a torque or twisting force on the reinforcement cage. This torquing of the reinforcement cage may break or untwist the tie-wires holding the spacers to the reinforcement cage, causing them to become unstable and lay over, which allows the reinforcement cage to shift or twist out of proper position. Thus, the reinforcement cage can become uncentered within the excavated shaft.
Additionally, such spacers are still difficult, labor intensive and time consuming to install as they must be tied at several points to the reinforcement cage structure to secure the spacers thereto. Additionally, the tie-wire connectors for these spacers can easily rust and become brittle and therefore can easily break during attachment of the spacers to the reinforcement cage or as stresses are placed on the spacers during insertion of the reinforcement cage and pouring of concrete into the excavated shaft.
Another problem with this type sled spacer is that it is relatively heavy, which requires increased shipping costs.
Further, the installation of the sled spacers which are tied to the cage is labor intensive.
Accordingly, it can be seen that it would be desirable to provide reinforcement cages for concrete structures having spacers which maintain the reinforcement cage in a centralized position within an excavated shaft for the concrete structure, and which is easy to install and use and which resists the torque or twisting forces exerted on the reinforcement cage during the insertion of the reinforcement cage into the excavated shaft and during the pouring of concrete therein.